Single channel two-way communication system



April 30, g40. w, R, KOCH 2.199.179

SINGLE CHANNEL TWO-WAY COMMUNICATION SYSTEM Qttomeg SINGLE CHANNEL TWO-WAY COMMUNICATION SYSTEM 'Filed Nov, 27. 1936 3 Sheets-Sheet 2 E is; a- 97 I gnventor mff: d Koch Gttorneg Patented Ar. 30, 194() STTES SINGLE CHANNEL TWO-WAY COMMUNICA- TION SYSTEM Winfield R. Koch, Merchantville, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application November 27, 1936, Serial No. 113,035

8 Claims.

My invention relates to a single channel two- Way communication system and more specifically to a two-way ultra high frequency radio telephone system.

I am aware that two-way communication systems have been used with a pair of signal channels. The transmitters are arranged to operate at substantially different frequencies, whereby interference effects are avoided. Such systems have the objectionable feature of requiring a pair of communication channels which must be taken from a limited number of channels.

Communication systems have been used in which a single channel is employed but the receiving station cuts 01T its carrier during periods of reception and restores the carrier during periods of transmission. T. propose to establish two-way communication on a single channel Without establishing undesired feedback eiects, and by alternately and automatically establishing the carrier for discrete periods from station to station.

One of the objects of my invention is to provide a method and means for establishing twoway communication over a single channel.

Another object is to provide a method and means for alternately and automatically establishing for discrete periods a carrier wave between stations in a communication system.

Another object is to provide means for automatically suppressing reception atthe transmitting station during periods of transmission, whereby feedback effects are avoided.

A further object is to provide a single source for automatically controlling discrete periods of carrier transmission from two or more stations in a communication system.

My invention may be best understood by referring to the accompanying drawings in which Fig. 1 is a schematic circuit diagram of one station for a communication system,

Fig. 2 is a schematic circuit diagram of a station which is associated with the station illustrated in Fig. 1 to form one embodiment of my invention,

Fig. 3 is a circuit diagram of an impulse generator,

Fig. 4 is a schematic illustration of the operation of the discrete carrier wave impulse employed in the communication system of my invention,

Fig. 5 is a circuit diagram of an impulse modulator, and

Fig. 6 is a schematic illustration of the sequence of events and the various timing im- (Cl. Z50-9) pulses present in the main and the auxiliary stations.

Referring to the circuit diagram (Fig. 1) which will hereafter be referred to as the main station, a carrier frequency generator I is coupled to a radio frequency amplifier 3. The radio frequency amplifier 3 is coupled to a second amplifier l which is coupled to an antenna system 9. The anode circuit of the second amplifier l includes a modulator il which is connected to a microphone I3 or any source of signals.

An impulse generator I5 is connected to a delay network il which comprises inductors i9, capacitors 2l, and a terminating resistor 23. A connection H35 is made from a point intermediate the ends of the delay network ll to an impulse modulator 25. The impulse modulator 25 is included in the anode circuit of the rst radio frequency amplifier 3. The input and the output of the delay network il are respectively' connected to impulse amplifiers 2l and 28 by leads HM and E06. The outputs of the impulse amplifiers 2l and 28 are connected in parallel and to a control grid of a radio frequency ampliiier 29 which is preferably connected between the antenna S and the radio receiver 3i. The radio receiver 3i may include a detector and audio frequency amplifier. The audio frequency amplifier output is impressed on telephones 33 or other signal indicator.

Before describing the operation of the main station, the schematic circuit arrangement of an auxiliary station will be considered. Fig. 2 is the circuit diagram of an auxiliary station which is not unlike the main station. In the auxiliary station, a carrier frequency generator 35 is coupled to a radio frequency amplifier 3l. The radio frequency amplifier 3l is coupled to a second radio frequency amplifier 39 which is coupled to an antenna system di. The anode circuit of the second radio frequency amplifier 39 includes a modulator d3. A microphone l5 is connected to the input of the modulator t3.

The receiver il at the auxiliary station is coupled to the antenna il by a radio frequency amplifier 69. The receiver dl includes a detector which is connected to an impulse frequency amplifier 5I and to an audio frequency amplifier 53. 'Ihe audio frequency output is impressed on telephones 55 or the like. The output of the impulse frequency amplifier 5l is connected to a delay network 51 which is comprised of inductors 59, capacitors 6l, and a terminating resistor 63. 'Ihe rst and third sections of the delay network are connected to an impulse amplier 65 by leads |0| and |03, respectively. 'I'he output circuit of the impulse amplifier 65 is connected between the cathode and a control grid of the radio frequency amplifier 49. A connection |02 is made from the second section of the delay network 51 to the input of an impulse modulator 61. The output of the impulse modulator 61 is connected in the anode circuit of the first radio frequency amplifier 31.

The operation of the system is dependent upon the impulses created by an impulse generator. One form of impulse generator circuit is illustrated in Fig. 3, in which the thermionic tube 1| is connected as an oscillator. The grid circuit comprises an inductor 13 which is coupled through a grid capacitor 15 to the grid electrode 11. The grid electrode is connected to cathode 19 through an adjustable grid-leak resistor 8l. The anode 83 is connected through an inductor 85, which is mutually coupled to the grid inductor 13, and through a resistor 81 to the positive terminal of a B battery 89. The output currents flowing through resistor 81 establish impulses which may be further amplified and phased by one or more amplifiers 9|. The oscillator starts to generate oscillatory currents butthe values of the associated elements, in particular the capacitor 15 and grid resistor 8|, are chosen so that the oscillator blocks. The charge on the grid capacitor 15 leaks 01T through the grid resistor 8| to ground, and again the oscillator starts. These cycles continue and form on impulses for a discrete period and discrete off intervals. I prefer to generate the off intervals and on impulses at a superaudible rate.

Figure 5 shows one form of impulse modulator which is found in Patent No. 1,631,670, issued June 7, 1927, to I. F. Byrnes. The impulse Voltage is applied to the input of a thermionic tube |09 through a transformer III. The grid electrode |01 is connected through transformer Il! and a biasing battery ||5 to the cathode ||9. Anode potential is supplied by a battery ||1, or the like. The cathode ||9 is connected to the anode of the controlled amplifier 3 through the primary |2| of the coupling transformer |23. The cathode potential of the modulator tube |09 is the source of the voltage for energizing the anode of amplifier tube 3.

In operation, the tube |09 is normally biased to cut-olf. A positive impulse from the time delay network decreases the negative cathode-togrid bias, causing the tube to draw anode current. Consequently, the potential of cathode 9 becomes positive with respect to ground, and a positive potential is impressed on the anode of amplifier 3, so that a signal impulse is passed to amplifier 1.

Referring to Figs. 1 and 2, assuming the impulse generator I5 is operating at the start of an on impulse. This impulse is first transferred by lead |04 through the impulse amplifier 28 in a phase which biases the control grid of amplifier 29 to cut-off. After a slight delay the on impulse is impressed on the impulse modulator 25 by connector |05. The impulse modulator 25 is arranged to supply the anode current for the radio frequency amplifier 3 for the duration of the on impulse. Since the anode current is thus supplied, the carrier currents from carrier generator will be transferred through the first amplifier 3 to the second amplifier 1. The output currents of the second amplifier 1 are impressed on the antenna 9 and radiated. If a signal is impressed on the microphone I3 during the on impulse, the signal currents from the microphone are amplified by the modulator and thereby vary the amplitude of the carrier currents.

When the first delayed on impulse from |05 ceases, the carrier is no longer transferred, and modulation currents from the microphone |3 have no effect. Before the original impulse stops, however, the second delayed impulse from the second section of the delay circuit |1 is applied to the impulse amplifier by lead |06. The amplifier 29, therefore, remains oi. In the meantime, the delayed impulse which turned the carrier on ceases. Therefore, the receiver is shut off by the two subsequent impulses for the full duration of the transmitter lon period. Finally, the impulse transferred by lead |06 to the amplifier 21 is reduced to zero and thus the radio frequency amplifier 29 is restored to operating condition after the carrier has substantially completely died out. The impulse generator I5 being in the off cycle or interval, no carrier currents are radiated and the receiver 29, 3| is sensitive to incoming currents. This sequence is graphically represented by Fig. 6 at a to e.

The carrier waves, either modulated or unmodulated 93, are radiated from the main station antenna to the auxiliary station (see Fig. 4) These waves create carrier currents in the antenna at the auxiliary station (see Fig. 2). The received currents are amplified by the radio frequency tube 49 and the receiver 41. The amplified currents which are detected by the receiver include two components: First, the discrete on impulses, and second, the signal impulses. The on impulses are amplified by the impulse frequency amplifier 5| and are passed through the delay network 51.

The delay network 51 at the auxiliary station operates over a longer time interval than the delay network |1 at the main station. The delay network 51 preferably has three distinct periods. The first period operates by lead |0| to impress currents through the impulse amplifier 66 to cut off the amplifier 49 just after the received on impulse ceases. The second period starts as soon as the amplifier has been cut off, and provides an impulse which is impressed by lead |02 through the impulse modulator B1 on the first radio frequency amplifier 31. Irregularities in the wave form of this impulse may be smoothed out or eliminated by a limiting device located within the impulse modulator 61. This impulse is phased to supply anode current to the anode circuit of the amplifier for a time period which is substantially equal to the period of the on impulses at the main station but these on impulses at the auxiliary transmitter are so delayed that they occur during the off intervals of the carrier impulses at the main transmitter.

During the on" periods at the auxiliary station, the modulator 43 may be operated to modulate the carrier frequency currents from generator 35 which are transferred through the rst 31 and second 39 radio frequency amplifiers to the antenna 4|. The radiated carrier Waves, modulated 91 and unmodulated 99, are illustrated in Fig. 4. The third delay period, connector |03, is used to continue the cut-off bias on the radio amplifier 49 at the receiver until the carrier at the auxiliary station has substantially completely died out. During the off intervals at the auxiliary station, the radio frequency amplifier 49 is in operating condition to transfer signals impressed on the antenna 4| to the receiver 41 in iii the conventional manner. This sequence of events is graphically illustrated by Fig. 6, f to l.

Thus, I have described a two-way communication system in which a single carrier Wave is transmitted from a main station to an auxiliary station during discrete periods which preferably occur at a superaudible rate. During intervals when the main station carrier is not radiated, the carrier from the auxiliary station is radiated. During the period of carrier radiation from either station, the receiver at that station is rendered inoperative whereby feedback and blocking effects may be eliminated. While the signal frequencies are not fully transmitted, I have found that the details omitted during the o intervals are hardly noticeable because of the superaudible rate at which discrete groups of carrier waves are radiated.

While I have described the modulators as operating in the anode circuits of the several tubes, it will be understood by those skilled in the art that grid modulation may be used. likewise, while the carrier radiation is described as modulated or unmodulated, the carrier may be suppressed at the auxiliary station during periods of no modulation by methods which are familiar to those skilled in the art. In installations where feedback and blocking effects are negligible, the one or more of the connections from the delay net- Works to the radio frequency amplifier in the receivers may be omitted. In some instances the delay network at the main station may be completelyomitted, and a single delay network employed to phase the radiation of the carrier at the auxiliary station. The main and auxiliary carrier generators do not have to be synchronized because they are never radiated at the same time. It should also be understood that my invention is not limited to the impulse generator illustrated in as much as any means of timing the discrete periods of transmission may be used. The system described is not limited to a main station and one auxiliary station. A plurality of auxiliary stations may be used to transmit carriers during successive intervals concurrent with the off intervals of the main carrier Wave.

l'. claim as my invention:

.1. The method of communication between a main station and an auxiliary station which comprises radiating a carrier wave from said main station for discrete periods separated by discrete intervals, receiving said radiated carrier at said auxiliary station, radiating a carrier wave from said auxiliary station during a portion or the interval between said discrete periods, receiving said carrier wave from said auxiliary station at said main station during said portion of the interval between said discrete periods when no carrier is radiated from said main station, controlling the operation of said auxiliary station by successively delaying a controlling impulse derived from the carrier radiated from said main station, applying an intermediate period of said delayed controlling impulse to cause radiation from said auxiliary station, and applying prior and subsequent periods of said delayed controlling impulse to limit reception of said main carrier at said auxiliary station.

2. The method of communication between a main station and an auxiliary station which comprises radiating a carrier wave from said main station during discrete periods which recur at a superaudible rate, receiving said radiated carrier at said auxiliary station, radiating a carrier wave from said auxiliary station during a portion of the interval between said discrete periods, receiving the carrier wave from said auxiliary station during said portion of the interval between said discrete periods, controlling the operation of said auxiliary station by successively delaying a controlling impulse derived from the carrier radiated from said main station, applying an intermediate period of said delayed controlling impulse to cause radiation from said auxiliary station, and applying prior and subsequent periods of said delayed controlling impulse to limit reception of ods, cutting oi said carrier when the carrier from said main station is being received at said auxiliary station, modulating said auxiliary carrier, radiating said modulated carrier during a portion of said discrete interval when said carrier is cut ofi at said main station, limiting the radiation of said carrier from said auxiliary station to the poi'- tion of said discrete interval 'by one of a series of differently timed controlling impulses, and limiting the reception at said auxiliary station by other and diiierently timed impulses.

5. The method of communication between a main station and an auxiliary station which comprises generating a carrier current at said main station, generating a plurality of discrete. irnpulses at a superaudible rate, successively delaying said discrete impulses to obtain a series of differently timed discrete impulses, controlling the radiation of said carrier from said main station by one of said series of diierently timed discrete impulses, whereby said carrier is radiated for discrete periods and is cut off for discrete intervals, receiving said radiated carrier at said auxiliary station, generating a carrier at said auxilary staton, radiating said carrier from said auxiliary station for discrete periods within said cut-oir intervals at said main station, said radiation from said auxiliary station being controlled by deriving an impulse from the carrier received at said auxiliary station, successively delaying said derived impulse to obtain a series of discrete impulses, and applyng one of said delayed impulses to cause radiation from said auxiliary station, and applying prior and subsequent impulses to shut off reception at said auxiliary station for a period concurrent with but slightly exceeding said period of transmission at said auxiliary station.

6. The method of communication between a main station and an auxiliary station which comprises generating a carrier current at said main station, generating a plurality of discrete impulses at a superaudible rate, successively delaying said discrete impulses to obtain a series of differently timed discrete impulses, controlling the radiation of said carrier from said main station by one of said series of differentially timed discrete impulses, whereby said carrier is radiated for discrete periods and is cut oi for discrete intervals, receiving said radiated carrier at said auxiliary station, generating a carrier at said auxiliary station, radiating said carrier from said auxiliary station for discrete periods which occur during said cut-off intervals at said main station, interrupting reception at said main station when said carrier is radiated therefrom by successively delaying said discrete impulses to obtain a series of discrete impulses starting at successive time intervals, applying an intermediate impulse to control the on periods of said carrier and applying prior and subsequent impulses to shut off reception at said main station for a period concurrent with but slightly exceeding said period of transmission, said radiation from said auxiliary station being controlled by deriving an impulse from the carrier received at said auxiliary station, successively delaying said derived impulse to obtain a series of discrete impulses, and applying one of said delayed impulses to cause radiation from said auxiliary station, and applying prior and subsequent impulses to shut oil' reception at said auxiliary station for a period concurrent with but slightly exceeding said period of transmission at said auxiliary station.

'1. A communication system comprising a main station and an auxiliary station, said main station comprising means for generating a carrier current, means for generating impulses at a superaudible rate and corresponding to discrete on periods and discrete oi intervals, means including said impulse generating means for interrupting said carrier current, means for modulating said carrier, means for radiating said carrier during said discrete on periods, means for receiving at said station, a delay circuit connected to saidv impulse generating means, and means connected between said delay circuit and said receiver whereby said receiver is cut 01T during said on periods, and is restored during said oiI intervals, said auxiliary station comprising means for receiving the carrier radiated from said main station, means for deriving impulses from said received carrier, means for delaying said derived impulses until the on impulse at the auxiliary station corresponds to the H interval at said main station, means for generating a carrier current at said auxiliary station, means for radiationg said carrier from said auxiliary station, and a connection from said delay means to conne the radiation of said carrier from said auxiliary station to periods corresponding substantially to the ofI" intervals at said main station.

8. A communication system comprising a main station and an auxiliary station, said main station comprising means for generating a carrier current, means for generating impulses at a superaudible rate and corresponding to discrete on" periods and discrete "oi" intervals, means including said impulse generating means for interrupting said carrier current, means for modulating said carrier, means for radiating said carrier during said discrete on periods, means for receiving at said station, a delay circuit connected to said impulse generating means, .and means connected between said delay circuit and said receiver whereby said receiver is cut oi during said on periods, and is restored during said oil intervals, said auxiliary station comprising means for receiving the carrier radiated from said main station, means for deriving impulses from said received carrier, means for delaying said derived impulses until the on impulse at the auxiliary station corresponds to the oil interval at said main station, means for generating a carrier` current at said auxiliary station, means for radiating said carrier from said auxiliary station, a connection from said delay means to conne the radiation of said carrier from said auxiliary station to periods corresponding substantially to the off intervals at said main station, and a connection from said delay means and said means for receiving said auxiliary station to cut oi the receiver at said auxiliary station during periods during which the carrier is radiated from said auxiliary station.

WINFIELD R. KOCH. 

